As a chemical power source, a Lithium ion battery is referred to as a secondary battery comprising a cathode formed from a compound able to reversibly intercalate and de-intercalate lithium ion, and an anode formed from other compound(s) able to reversibly intercalate and de-intercalate lithium ion. When the battery is charged, Lithium ion is de-intercalated from its cathode and intercalated into its anode. The reverse takes place when the battery is discharged. A lithium ion battery basically comprises an electrode core and a nonaqueous electrolyte, both sealed in the battery case. The electrode core comprises a battery electrode comprising an anode, a cathode and a membrane used to separate the anode from the cathode. The cathode comprises a current collector and a cathode material coated on and/or filled in the current collector. The cathode material comprises a cathode active substance, a conductive additive and an adhesive.
It is known that the cycling performance of a battery basically depends on reversibility and structural stability of the cathode active substance in a lithium ion battery during lithium ion intercalation and de-intercalation. The conventional anode active substance that can reversibly intercalate and de-intercalate in this field comprises LixNi1−yCoO2, wherein 0.9≦x≦1.1, 0≦y≦1.0; Li1+aMbMn2−bO4, wherein −0.1≦a≦0.2, 0≦b≦1.0, M is one of Li, B, Mg, Al, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, F, I and S; and LimMn2−nBnO2, wherein 0.9≦m≦1.1, 0≦n≦1.0, and B is a transition metal. The lithium ion battery which comprises the above-mentioned material especially lithium manganate (LiMn2O4) as a cathode active substance has a lower specific capacity and the capacity of the battery decreases rapidly with the increase of cycle number of charge-discharge of the battery, whereby resulting in a lower cycling performance of the battery.
It is found after research that the main reason for the lower cycling performance of the Lithium ion battery is that the characteristic of the anode active substance has changed due to the reaction between the anode active substance and electrolyte. At present, in order to improve the cycling performance of the battery, a lot of studies on surface treatment to cathode active substance especially to lithium manganate in the lithium ion battery to prevent the reaction between the cathode active substance and electrolyte have been given.
For example, U.S. Pat. No. 5,783,328 discloses a process of treating lithium manganese represented by the stoichiometric formula LixMn2O4+d (wherein 0.9≦x≦1.2 and 0≦d≦0.4). The process involves the steps of a) treating said lithium manganese oxide particles with at least one water soluble metal salt of a carboxylic acid to form a coating of said metal salt on the surface of said particles, and b) heating said treated lithium manganese oxide particles in an atmosphere comprising carbon dioxide gas for 1-20 hours.
By means of coating metal carbonate on the surface of lithium manganate, the cycling performance of the resulted lithium ion battery with this lithium manganate is improved. However, the specific capacity of this lithium ion battery is lowered since metal carbonate cannot act as an anode active substance.